trans-Fatty acid consumption and its association with distal colorectal cancer in the North Carolina Colon Cancer Study II

Associations of dietary fat types (MUFA, PUFA, SFA) and sources (animal, plant) with colorectal cancer risk: A comprehensive systematic review and dose-response meta-analysis of prospective cohort studies

BACKGROUND AND OBJECTIVES

While dietary fat intake has long been implicated as a risk factor for colorectal cancer, evidence from prospective cohort studies remains inconsistent. Moreover, previous meta-analyses examining the link between dietary fat intake and risk of colorectal cancer have not explored the dose-response relationships. Therefore, the current systematic review and meta-analysis was conducted to assess the dose-response associations of intakes of specific types (MUFA, PUFA and SFA) and sources (animal, plant) of dietary fat with the risk of colorectal, colon or rectal cancer.

METHODS

A comprehensive literature search of relevant online databases was performed to detect eligible studies until May 2023, identifying 21 prospective cohort studies with a total sample size of 2311,737 participants. The follow-up periods ranged from 7 to 19.4 years, during which 21,125 cases of colorectal, colon or rectal cancer were recorded.

RESULTS

Comparing extreme intake levels of total fat revealed the summary relative risk (RR) of 1.05 (95 % CI: 0.96-1.15) for colorectal cancer, 0.99 (95 % CI: 0.87-1.11) for colon cancer, and 1.09 (0.95 % CI: 0.93-1.13) for rectal cancer, indicating no significant association. Neither animal nor plant fat intake was associated with the risk of cancers. While no significant findings were also observed for MUFA or PUFA, the highest versus lowest comparison showed that a high intake of SFA was associated with a reduced risk of both colorectal 0.91 (95 % CI: 0.85-0.99) and colon cancer 0.86 (95 % CI: 0.75-0.98). However, in the non-linear dose-response analysis, the inverse association was seen within a certain range (<40 g/day).

CONCLUSIONS

These findings suggest that dietary SFA intake, less than 40 g/day, may have a protective effect against colorectal cancer. Further studies are needed to confirm our findings.

Dietary trans fatty acids and risk of colorectal cancer: a systematic review and meta-analysis of observational studies

PURPOSE

Although trans fatty acid has been associated with diabetes and cardiovascular disorders, studies gave conflicting results when examined their impact on colorectal cancer (CRC). The present systematic review and meta-analysis aimed to summarize the current evidence regarding the association between dietary and tissue trans fatty acids and the risk of CRC.

METHODS

We searched PubMed/MEDLINE, EMBASE, Scopus, Web of Science (ISI), and Google Scholar without date and language limitation up to May 2022 and included the eligible studies. The quality of included studies was assessed using the Newcastle-Ottawa scale. The overall odds ratios (ORs) were derived using a random-effects model.

RESULTS

In assessment of dietary trans fatty acids 18 studies, including eight cohort, 10 case-control, and observational data from one randomized control trial were included. Although Dietary trans fats were associated with higher risk of CRC (OR = 1.093, 95% CI 1.017, 1.176, P = 0.016; I² = 61.3%), Subgroup analysis by study design yielded an insignificant effect for case-control (OR = 1.152, 95% CI 1.000, 1.328, P = 0.050; I² = 77.2%) and cohort (OR = 1.027, 95% CI 0.976, 1.081, P = 0.299; I² = 0%) studies. Although there was no significant association of trans fatty acids with rectal cancer (OR = 1.093, 95% CI 0.984 to 1.215, P = 0.098; I² = 0%), there was for colon cancer (OR = 1.91, 95% CI 1.062 to 1.335, P = 0.003; I² = 37.6%).The analysis of four studies that evaluated the relation between tissue trans fat and CRC revealed meaningful result (OR = 0.745, 95% CI 0.619, 0.896, P = 0.002; I² = 42.6%). While subgroup assessments for colon cancer (OR = 0.804, 95% CI 0.583, 1.109, P = 0.183; I² = 0%) and plasma trans fatty acids OR = 0.853, 95% CI 0.633, 1.150, P = 0.298; I² = 0%) were insignificant.

CONCLUSION

Dietary trans fatty acids increased the risk of CRC, whereas tissue trans fatty acids had a protective effect on CRC. Nonetheless, neither type of trans fatty acid increased the risk of colon or rectal cancer; thus, more prospective studies are needed to determine the validity of these associations.

Possible role of nutrition in the prevention of inflammatory bowel disease-related colorectal cancer: A focus on human studies

Patients with inflammatory bowel disease (IBD) are at substantially high risk for colorectal cancer (CRC). IBD-associated CRC accounts for roughly 10% to 15% of the annual mortality in patients with IBD. IBD-related CRC also affects younger patients compared with sporadic CRC, with a 5-y survival rate of 50%. Regardless of medical therapies, the persistent inflammatory state characterizing IBD raises the risk for precancerous changes and CRC, with additional input from several elements, including genetic and environmental risk factors, IBD-associated comorbidities, intestinal barrier dysfunction, and gut microbiota modifications. It is well known that nutritional habits and dietary bioactive compounds can influence IBD-associated inflammation, microbiome abundance and composition, oxidative stress balance, and gut permeability. Additionally, in recent years, results from broad epidemiologic and experimental studies have associated certain foods or nutritional patterns with the risk for colorectal neoplasia. The present study aimed to review the possible role of nutrition in preventing IBD-related CRC, focusing specifically on human studies. It emerges that nutritional interventions based on healthy, nutrient-dense dietary patterns characterized by a high intake of fiber, vegetables, fruit, ω-3 polyunsaturated fatty acids, and a low amount of animal proteins, processed foods, and alcohol, combined with probiotic supplementation have the potential of reducing IBD-activity and preventing the risk of IBD-related CRC through different mechanisms, suggesting that targeted nutritional interventions may represent a novel promising approach for the prevention and management of IBD-associated CRC.

Comprehensive Investigation on Associations between Dietary Intake and Blood Levels of Fatty Acids and Colorectal Cancer Risk

BACKGROUND

Increasingly, studies have discovered that different fatty acids (Fas) are linked to colorectal cancer (CRC) risk.

METHODS

We systematically searched Embase and Medline databases to identify eligible studies that examined the associations of different types of Fas with CRC risk. The effect estimates and their 95% confidence intervals (Cis) were pooled using a random-effects model. Subgroup and sensitivity analyses were performed to examine the robustness of the study findings.

RESULTS

This study evaluated the associations of 28 dietary and 18 blood Fas with CRC risk by summarizing the most updated evidence from 54 observational and four Mendelian Randomization (MR) studies. The present findings suggested that high dietary intake of eicosapentaenoic acid (EPA), docosahexanoic acid (DHA), and docosapentaenoic acid (DPA) are related to low risk of CRC, while the n-6/n-3 PUFA ratio and trans-FA are related to high risk of CRC. The summary of all cohort studies found that a high intake of SFA and DHA was a protective factor for CRC, and a high intake of the n-6/n-3 PUFA ratio was a risk factor for CRC. In the subgroup analysis of cancer subsites, we found that the dietary intake of linoleic acid (LA) and trans-FA are risk factors, while DPA is a protective factor for colon cancer. High dietary DHA intake was associated with a lower risk of rectal cancer, while the dietary n-6/n-3 PUFA ratio was associated with a higher risk of rectal cancer. Meta-analysis of blood FA levels showed a significant reverse association between blood pentadecanoic acid and CRC risk, whilst other blood Fas showed no significant association with CRC risk. All included MR studies showed that high plasma arachidonic acid (AA) is associated with increased CRC risk.

CONCLUSIONS

Current evidence on the dietary intake and blood levels of Fas in relation to CRC risk is less consistent. Future studies are needed to investigate how the metabolism of Fas contributes to CRC development.

Dietary Ruminant and Industrial Trans-Fatty Acids Intake and Colorectal Cancer Risk

As colorectal cancer (CRC) is largely due to modifiable lifestyle habits, the awareness on its risk factors is highly important. Dietary fatty acids have been linked to CRC risk. We explored the association between dietary trans fatty acids (TFAs) intake and CRC risk. We analyzed 865 CRC cases (434 in colon and 404 in rectum) and 3206 controls of the IROPICAN study, with data collected by trained interviewers using validated questionnaires. TFAs intake (industrial and ruminant types) was categorized into quartiles. Multivariate logistic regression models were built to calculate the odds ratios (OR) for the association between CRC and TFAs. We observed a positive association between industrial TFAs and colon cancer (OR for highest vs lowest quartile [ORQ4vsQ1] = 1.28, 95% confidence interval 1.07-1.54). A higher association was observed between industrial TFAs and CRC, occurring after 50 years of age. In addition, elaidic acid was associated with an increased risk of colon (ORQ4vsQ1 = 1.58, 1.24-2.02) and specifically of proximal colon cancer (OR Q4vsQ1 = 2.12, 1.40-3.20), as well as of rectum cancer (ORQ4vsQ1 = 1.40, 1.07-1.83). An inverse association was observed between ruminant TFAs intake and colon cancer risk (ORQ4vsQ1 = 0.80, 0.67-0.97). Industrial TFAs, such as semisolid/solid hydrogenated oils, may increase the risk of CRC, especially colon and proximal colon cancer. In contrast, ruminant TFAs do not appear to be associated with CRC. Awareness programs and regulatory actions regarding hydrogenated oils are warranted, given their high consumption through ultra-processed foods in more developed and less developed countries.

Interactions of Colorectal Cancer, Dietary Fats, and Polymorphisms of Arachidonate Lipoxygenase and Cyclooxygenase Genes: A Literature Review

Objective

Genetics and dietary factors play important roles in the development of colorectal cancer (CRC). However, the underlying mechanisms of the interactions between CRC, gene polymorphisms, and dietary fat are unclear. This review study investigated the effects of polymorphisms of arachidonate lipoxygenase (ALOX) and cyclooxygenase (COX) genes in the association between CRC and dietary fat.

Methods

All the related papers published from 2000 to 2022 were collected from different databases such as PubMed, Science Direct, Scopus, and Cochran using related keywords such as colorectal cancer, ALOX, COX, polymorphism, and dietary fat. Non-English and unrelated documents were excluded.

Results

Some single-nucleotide polymorphisms (SNPs) in the ALOX and COX genes, such as rs2228065, rs6413416, and rs4986832 in the ALOX gene, and rs689465 in the COX gene may play significant roles in the association between the risk of CRC and dietary fats. SNPs of ALOX and COX genes may influence the effects of dietary fatty acids on the risk of CRC.

Conclusion

Some polymorphisms of the ALOX and COX genes may have important roles in the effects of dietary fat on the risk of CRC. If future studies confirm these results, dietary recommendations for preventing colorectal cancer may be personalized based on the genotype of the ALOX and COX genes.

Key Markers Involved in the Anticolon Cancer Response of CD8+ T Cells through the Regulation of Cholesterol Metabolism

BACKGROUND

T cell-mediated antitumor immune response is the basis of colorectal cancer (CRC) immunotherapy. Cholesterol plays an important role in T cell signal transduction and function. Apolipoprotein E (APOE) plays a major role in cholesterol metabolism.

OBJECTIVE

To screen and analyze key markers involved in the anticolon cancer response of CD8+ T cells through the regulation of cholesterol metabolism.

METHODS

Based on the median cutoff of the expression value of APOE according to the data downloaded from The Cancer Genome Atlas and Gene Expression Omnibus database, patients were grouped into low and high expression groups. Differences in clinical factors were assessed, and survival analysis was performed. Differentially expressed genes (DEGs) in the high and low expression groups were screened, followed by the analysis of differences in tumor-infiltrating immune cells and weighted gene coexpression network analysis results. The closely related genes to APOE were identified, followed by enrichment analysis, protein-protein interaction (PPI) network analysis, and differential expression analysis. Immunohistochemical staining (IHC) was used to detect the expression of CD8 in CRC tissues.

RESULTS

There were significant differences in prognosis and pathologic_N between the APOE low and high expression groups. A total of 2,349 DEGs between the high and low expression groups were selected. A total of 967 genes were obtained from the blue and brown modules. The probability of distribution of CD8+ T cells differed significantly between the two groups, and 320 closely related DEGs of APOE were screened. Genes including the HLA gene family, B2M, IRF4, and STAT5A had a higher degree in the PPI network. GEO datasets verified the prognosis and the related DEGs of APOE. IHC staining verified the relationship between the distribution of CD8+ T cells and APOE expression.

CONCLUSION

Genes including the HLA gene family, B2M, IRF4, and STAT5A might be the key genes involved in the anticolon cancer response of CD8+ T cells through the regulation of cholesterol metabolism.

Dietary trans-fatty acid intake in relation to cancer risk: a systematic review and meta-analysis

CONTEXT

Apart from ruminant fat, trans-fatty acids are produced during the partial hydrogenation of vegetable oils, (eg, in the production of ultraprocessed foods). Harmful cardiovascular effects of trans-fatty acids are already proven, but the link with cancer risk has not yet been summarized.

OBJECTIVE

A systematic review (following PRISMA guidelines) - including observational studies on the association of trans-fatty acid intake with any cancer risk - was conducted, with no limitations on population types.

DATA SOURCES

The electronic databases PubMed and Embase were searched to identify relevant studies.

DATA EXTRACTION

This systematic review included 46 articles. Quality was assessed via the Newcastle-Ottawa scale. Meta-analyses were conducted if at least 4 articles exploring the same transfat-cancer pairings were found.

DATA ANALYSIS

Nineteen cancer types have been researched in cohort and case-control studies on trans-fatty acids, with breast cancer (n = 17), prostate cancer (n = 11), and colorectal cancer (n = 9) as the most researched. The meta-analyses on total trans-fat showed a significant positive association for prostate cancer (odds ratio [OR] 1.49; 95%CI, 1.13-1.95) and colorectal cancer (OR 1.26; 95%CI, 1.08-1.46) but not for breast cancer (OR 1.12; 95%CI, 0.99-1.26), ovarian cancer (OR 1.10; 95%CI, 0.94-1.28), or non-Hodgkin lymphoma (OR 1.32; 95%CI, 0.99-1.76). Results were dependent on the fatty acid subtype, with even cancer-protective associations for some partially hydrogenated vegetable oils. Enhancing moderators in the positive transfat-cancer relation were gender (direction was cancer-site specific), European ancestry, menopause, older age, and overweight.

CONCLUSION

Despite heterogeneity, higher risk of prostate and colorectal cancer by high consumption of trans-fatty acids was found. Future studies need methodological improvements (eg, using long-term follow-up cancer data and intake biomarkers). Owing to the lack of studies testing trans-fatty acid subtypes in standardized ways, it is not clear which subtypes (eg, ruminant sources) are more carcinogenic.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42018105899.

Dietary intake and plasma phospholipid concentrations of saturated, monounsaturated and trans fatty acids and colorectal cancer risk in the European Prospective Investigation into Cancer and Nutrition cohort

Epidemiologic studies examining the association between specific fatty acids and colorectal cancer (CRC) risk are inconclusive. We investigated the association between dietary estimates and plasma levels of individual and total saturated (SFA), monounsaturated (MUFA), industrial-processed trans (iTFA), and ruminant-sourced trans (rTFA) fatty acids, and CRC risk in the European Prospective Investigation into Cancer and Nutrition (EPIC). Baseline fatty acid intakes were estimated in 450 112 participants (6162 developed CRC, median follow-up = 15 years). In a nested case-control study, plasma phospholipid fatty acids were determined by gas chromatography in 433 colon cancer cases and 433 matched controls. Multivariable-adjusted hazard ratios (HRs) and odds ratios (ORs) with 95% confidence intervals (CIs) were computed using Cox and conditional logistic regression, respectively. Dietary total SFA (highest vs lowest quintile, HRQ5vsQ1  = 0.80; 95%CI:0.69-0.92), myristic acid (HRQ5vsQ1  = 0.83, 95%CI:0.74-0.93) and palmitic acid (HRQ5vsQ1  = 0.81, 95%CI:0.70-0.93) were inversely associated with CRC risk. Plasma myristic acid was also inversely associated with colon cancer risk (highest vs lowest quartile, ORQ4vsQ1  = 0.51; 95%CI:0.32-0.83), whereas a borderline positive association was found for plasma stearic acid (ORQ4vsQ1  = 1.63; 95%CI:1.00-2.64). Dietary total MUFA was inversely associated with colon cancer (per 1-SD increment, HR1-SD  = 0.92, 95%CI: 0.85-0.98), but not rectal cancer (HR1-SD  = 1.04, 95%CI:0.95-1.15, Pheterogeneity  = 0.027). Dietary iTFA, and particularly elaidic acid, was positively associated with rectal cancer (HR1-SD  = 1.07, 95%CI:1.02-1.13). Our results suggest that total and individual saturated fatty acids and fatty acids of industrial origin may be relevant to the aetiology of CRC. Both dietary and plasma myristic acid levels were inversely associated with colon cancer risk, which warrants further investigation.

Dietary Fat and Cancer-Which Is Good, Which Is Bad, and the Body of Evidence

A high-fat diet (HFD) induces changes in gut microbiota leading to activation of pro-inflammatory pathways, and obesity, as a consequence of overnutrition, exacerbates inflammation, a known risk factor not only for cancer. However, experimental data showed that the composition of dietary fat has a greater impact on the pathogenesis of cancer than the total fat content in isocaloric diets. Similarly, human studies did not prove that a decrease in total fat intake is an effective strategy to combat cancer. Saturated fat has long been considered as harmful, but the current consensus is that moderate intake of saturated fatty acids (SFAs), including palmitic acid (PA), does not pose a health risk within a balanced diet. In regard to monounsaturated fat, plant sources are recommended. The consumption of plant monounsaturated fatty acids (MUFAs), particularly from olive oil, has been associated with lower cancer risk. Similarly, the replacement of animal MUFAs with plant MUFAs decreased cancer mortality. The impact of polyunsaturated fatty acids (PUFAs) on cancer risk depends on the ratio between ω-6 and ω-3 PUFAs. In vivo data showed stimulatory effects of ω-6 PUFAs on tumour growth while ω-3 PUFAs were protective, but the results of human studies were not as promising as indicated in preclinical reports. As for trans FAs (TFAs), experimental data mostly showed opposite effects of industrially produced and natural TFAs, with the latter being protective against cancer progression, but human data are mixed, and no clear conclusion can be made. Further studies are warranted to establish the role of FAs in the control of cell growth in order to find an effective strategy for cancer prevention/treatment.

Dietary fatty acids modulation of human colon cancer cells: mechanisms and future perspectives

Colorectal cancer (CRC) is one of the most common malignancies worldwide and its pathogenesis is proven to be related with dietary patterns, namely dietary fatty acid (FA) intake. We reviewed the evidences regarding the effect of different dietary FAs on human CRC cell lines proliferation and apoptosis. Altogether, the results obtained from in vitro studies show that monounsaturated FAs lack evidence regarding both proliferation and apoptosis, whereas there is a consensus about the anti-proliferative and pro-apoptotic effects, involving different intracellular targets, of n-3 polyunsaturated FAs, while n-6 series show a similar effect or no effects. The response to these dietary components depends on the cell type as well as the amount and duration of exposure. These results highlight the importance of identifying molecular targets for dietary components aiming to interfere with one of the main risk factors related with CRC incidence and prevalence.

Plasma trans-fatty acids levels and mortality: a cohort study based on 1999-2000 National Health and Nutrition Examination Survey (NHANES)

Background

Trans-fatty acids (TFAs) occur in small amounts in nature but became widely produced by the food industry. The hazardous effects of different TFA subtypes to human health are controversial. We aimed to evaluate the association of plasma TFAs levels (elaidic acid, vaccenic acid, palmitelaidic acid, and linoelaidic acid) with mortality.

Methods

Utilizing 1999–2000 Nutrition Examination Survey (NHANES) and linked mortality data, we performed a cohort study with 1456 participants and used Cox proportional hazards models and penalized smoothing spline plots to elucidate the relationships between TFAs and all-cause, cardiovascular diseases (CVD) and cancer mortality.

Results

During 16,034 person-years of follow-up, a total of 221 deaths occurred. In the multivariate model, including mutual adjustment for the 4 TFA subtypes, elaidic acid associated with higher all-cause mortality (hazard ratio (HR) = 2.00, 95% confidence interval (CI) = 1.18 to 3.40, fourth quartiles versus second quartiles) and CVD mortality (HR = 1.64, 95% CI = 1.07 to 2.50, per 10 units increase). Higher palmitelaidic acid levels were associated with increased cancer mortality (HR = 2.91, 95% CI = 1.09 to 7.81, fourth quartiles versus second quartiles). A J-shaped pattern was observed in the regression curve of elaidic acid and all-cause mortality, as well palmitelaidic acid and cancer mortality.

Conclusions

Plasma elaidic acid levels are associated with higher risk of all-cause and CVD mortality, and palmitelaidic acid levels are associated with higher cancer mortality in later life. Further studies are needed to investigate current inconsistent results in this field and the possible underlying mechanisms.

Electronic supplementary material

The online version of this article (10.1186/s12944-017-0567-6) contains supplementary material, which is available to authorized users.

The effects of trans-fatty acids on TAG regulation in mice depend on dietary unsaturated fatty acids

The aim of this study was to investigate the effects of trans-fatty acids (TFA) on liver and serum TAG regulation in mice fed diets containing different proportions of n-3, n-6 and n-9 unsaturated fatty acids (UFA) from olive (O), maize (C) or rapeseed (R) oils partially substituted or not with TFA (Ot, Ct and Rt, respectively). Male CF1 mice were fed (30 d) one of these diets. The effects of the partial substitution (1 %, w/w) of different UFA with TFA on the activity and expression of hepatic enzymes involved in lipogenesis and fatty acids oxidation were evaluated, as well as their transcription factor expressions. Some of the mechanisms involved in the serum TAG regulation, hepatic VLDL rich in TAG (VLDL-TAG) secretion rate and lipoprotein lipase (LPL) activity were assessed. In liver, TFA induced an increase in TAG content in the Ot and Rt groups, and this effect was associated with an imbalance between lipogenesis and β-oxidation. In the Ot group, exacerbated lipogenesis may be one of the mechanisms responsible for the liver steatosis induced by TFA, whereas in Rt it has been related to a decreased β-oxidation, compared with their respective controls. The enhanced hepatic VLDL-TAG secretion in the Ot and Rt groups was compensated with a differential removal of TAG by LPL enzyme in extrahepatic tissues, leading to unchanged serum TAG levels. In brief, the effects of low levels of TFA on liver and serum TAG regulation in mice depend on the dietary proportions of n-3, n-6 and n-9 UFA.

N-3 fatty acids reduced trans fatty acids retention and increased docosahexaenoic acid levels in the brain

INTRODUCTION

The levels of docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6) are critical for the normal structure and function of the brain. Trans fatty acids (TFA) and the source of the dietary fatty acids (FA) interfere with long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis.

OBJECTIVES

The aim of this study was to investigate the effect of TFA supplementation in diets containing different proportions of n-9, n-6, and n-3 FA on the brain FA profile, including the retention of TFA, LC-PUFA levels, and n-6/n-3 PUFA ratios. These parameters were also investigated in the liver, considering that LC-PUFA are mainly bioconverted from their dietary precursors in this tissue and transported by serum to the brain. Also, stearoyl-CoA desaturase-1 (SCD1) and sterol regulatory element-binding protein-1c (SREBP-1c) gene expressions were evaluated.

METHODS

Male CF1 mice were fed (16 weeks) diets containing different oils (olive, corn, and rapeseed) with distinct proportions of n-9, n-6, and n-3 FA (55.2/17.2/0.7, 32.0/51.3/0.9, and 61.1/18.4/8.6), respectively, substituted or not with 0.75% of TFA. FA composition of the brain, liver, and serum was assessed by gas chromatography.

RESULTS

TFA were incorporated into, and therefore retained in the brain, liver, and serum. However, the magnitude of retention was dependent on the tissue and type of isomer. In the brain, total TFA retention was lower than 1% in all diets.

DISCUSSION

Dietary n-3 PUFA decreased TFA retention and increased DHA accretion in the brain. The results underscore the importance of the type of dietary FA on the retention of TFA in the brain and also on the changes of the FA profile.

Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies

OBJECTIVE

To systematically review associations between intake of saturated fat and trans unsaturated fat and all cause mortality, cardiovascular disease (CVD) and associated mortality, coronary heart disease (CHD) and associated mortality, ischemic stroke, and type 2 diabetes.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Medline, Embase, Cochrane Central Registry of Controlled Trials, Evidence-Based Medicine Reviews, and CINAHL from inception to 1 May 2015, supplemented by bibliographies of retrieved articles and previous reviews.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Observational studies reporting associations of saturated fat and/or trans unsaturated fat (total, industrially manufactured, or from ruminant animals) with all cause mortality, CHD/CVD mortality, total CHD, ischemic stroke, or type 2 diabetes.

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently extracted data and assessed study risks of bias. Multivariable relative risks were pooled. Heterogeneity was assessed and quantified. Potential publication bias was assessed and subgroup analyses were undertaken. The GRADE approach was used to evaluate quality of evidence and certainty of conclusions.

RESULTS

For saturated fat, three to 12 prospective cohort studies for each association were pooled (five to 17 comparisons with 90,501-339,090 participants). Saturated fat intake was not associated with all cause mortality (relative risk 0.99, 95% confidence interval 0.91 to 1.09), CVD mortality (0.97, 0.84 to 1.12), total CHD (1.06, 0.95 to 1.17), ischemic stroke (1.02, 0.90 to 1.15), or type 2 diabetes (0.95, 0.88 to 1.03). There was no convincing lack of association between saturated fat and CHD mortality (1.15, 0.97 to 1.36; P=0.10). For trans fats, one to six prospective cohort studies for each association were pooled (two to seven comparisons with 12,942-230,135 participants). Total trans fat intake was associated with all cause mortality (1.34, 1.16 to 1.56), CHD mortality (1.28, 1.09 to 1.50), and total CHD (1.21, 1.10 to 1.33) but not ischemic stroke (1.07, 0.88 to 1.28) or type 2 diabetes (1.10, 0.95 to 1.27). Industrial, but not ruminant, trans fats were associated with CHD mortality (1.18 (1.04 to 1.33) v 1.01 (0.71 to 1.43)) and CHD (1.42 (1.05 to 1.92) v 0.93 (0.73 to 1.18)). Ruminant trans-palmitoleic acid was inversely associated with type 2 diabetes (0.58, 0.46 to 0.74). The certainty of associations between saturated fat and all outcomes was "very low." The certainty of associations of trans fat with CHD outcomes was "moderate" and "very low" to "low" for other associations.

CONCLUSIONS

Saturated fats are not associated with all cause mortality, CVD, CHD, ischemic stroke, or type 2 diabetes, but the evidence is heterogeneous with methodological limitations. Trans fats are associated with all cause mortality, total CHD, and CHD mortality, probably because of higher levels of intake of industrial trans fats than ruminant trans fats. Dietary guidelines must carefully consider the health effects of recommendations for alternative macronutrients to replace trans fats and saturated fats.

Nutrients, foods, and colorectal cancer prevention

Diet has an important role in the development of colorectal cancer. In the past few decades, findings from extensive epidemiologic and experimental investigations have linked consumption of several foods and nutrients to the risk of colorectal neoplasia. Calcium, fiber, milk, and whole grains have been associated with a lower risk of colorectal cancer, and red meat and processed meat have been associated with an increased risk. There is substantial evidence for the potential chemopreventive effects of vitamin D, folate, fruits, and vegetables. Nutrients and foods also may interact, as a dietary pattern, to influence colorectal cancer risk. Diet likely influences colorectal carcinogenesis through several interacting mechanisms. These include the direct effects on immune responsiveness and inflammation, and the indirect effects of overnutrition and obesity-risk factors for colorectal cancer. Emerging evidence also implicates the gut microbiota as an important effector in the relationship between diet and cancer. Dietary modification therefore has the promise of reducing colorectal cancer incidence.

Dietary and biomarker estimates of fatty acids and risk of colorectal cancer

The associations between intake of or circulating fatty acids and risk of colorectal cancer (CRC) are unclear. We examined prospectively the associations between dietary or biomarker fatty acids and CRC. For 41,514 men and women, aged 40-69 years, baseline (1990-94) dietary intakes of fatty acids were estimated using a food frequency questionnaire and plasma phospholipid (PPL) fatty acids were measured for 4,205 participants including 395 CRC cases, according to a case-cohort design. Hazard ratios were computed using Cox regression adjusting for education, alcohol intake, smoking status, physical activity and total energy intake; and stratified for gender, ethnicity and family history of cancer, with age as the time scale. We assessed the heterogeneity of associations with colon and rectal cancers. PPL saturated fatty acids (SFAs) were positively associated with CRC risk, while total n-3 polyunsaturated fatty acids (PUFA) and long chain marine n-3 PUFAs showed inverse associations, significant only for 22:5 n-3. No significant associations were observed for dietary fatty acid intakes but positive associations with CRC of borderline significance were seen for both dietary and PPL linoleic acid. Positive associations with dietary palmitic acid (16:0), MUFAs and n-6 PUFAs were seen for rectal but not colon cancers. PPL 22:6 n-3 was inversely associated with rectal cancer. Limiting intakes of SFAs and MUFAs could be assisted by following existing guidelines to limit red and processed meats which are important sources in the Australian diet. Our observations regarding linoleic acid should be examined further.

miRNA expression in human intestinal Caco-2 cells is comparably regulated by cis- and trans-fatty acids

Trans-fatty acids are unsaturated fatty acids with at least one double bond in trans configuration. While their role in the development of coronary heart disease is broadly accepted, a potential impact of these fatty acids on colon carcinogenesis is still under discussion. MiRNAs are small non-coding RNAs that regulate the gene expression at a post-transcriptional level by inhibiting the translation of target mRNAs. We investigated the effect of 16 different C 18 fatty acid isomers on the expression of 84 cancer-related miRNAs in the human colorectal adenocarcinoma cell line Caco-2 by using a qRT-PCR array. 66 of these 84 miRNAs were deregulated by at least one fatty acid, however, there was no trans-specific impact on miRNA expression as the corresponding cis isomer of a given fatty acid generally had comparable effects on the miRNA expression profile. The most pronounced effects were observed for hsa-miR-146a-5p, which was upregulated by four of the 16 investigated fatty acids, and hsa-miR-32-5p, which was strongly downregulated by five fatty acids. As hsa-miR-32-5p was described to target genes being involved in the regulation of apoptosis, the effect of α-eleostearic acid on the expression of the apoptosis-associated genes BCL2L11, BCL-2, and BCL-XL was examined. The qPCR results indicate that fatty acid-mediated downregulation of hsa-miR-32-5p is accompanied by a downregulation of BCL-2 and BCL2L11 mRNA whereas BCL-XL was shown to be simultaneously upregulated. In conclusion, our data indicate that several fatty acids are able to regulate miRNA expression of human colon cancer cells. However, no trans-specific regulation was observed.

Current issues surrounding the definition of trans-fatty acids: implications for health, industry and food labels

The definition of trans-fatty acids (TFA) was established by the Codex Alimentarius to guide nutritional and legislative regulations to reduce TFA consumption. Currently, conjugated linoleic acid (CLA) is excluded from the TFA definition based on evidence (primarily preclinical studies) implying health benefits on weight management and cancer prevention. While the efficacy of CLA supplements remains inconsistent in randomised clinical trials, evidence has emerged to associate supplemental CLA with negative health outcomes, including increased subclinical inflammation and oxidative stress (particularly at high doses). This has resulted in concerns regarding the correctness of excluding CLA from the TFA definition. Here we review recent clinical and preclinical literature on health implications of CLA and ruminant TFA, and highlight several issues surrounding the current Codex definition of TFA and how it may influence interpretation for public health. We find that CLA derived from ruminant foods differ from commercial CLA supplements in their isomer composition/distribution, consumption level and bioactivity. We conclude that health concerns associated with the use of supplemental CLA do not repudiate the exclusion of all forms of CLA from the Codex TFA definition, particularly when using the definition for food-related purposes. Given the emerging differential bioactivity of TFA from industrial v. ruminant sources, we advocate that regional nutrition guidelines/policies should focus on eliminating industrial forms of trans-fat from processed foods as opposed to all TFA per se.

Ácidos graxos trans em produtos alimentícios brasileiros: uma revisão sobre aspectos relacionados à saúde e à rotulagem nutricional

Nos últimos anos, vários estudos apontam a relação positiva entre ácidos graxos trans e desenvolvimento de doenças cardiovasculares, materno-infantis, inflamatórias e de câncer. A Organização Mundial de Saúde alertou para a necessidade da diminuição do consumo desses ácidos graxos, o que culminou com a recomendação de sua eliminação em 2004. A rotulagem é uma medida que auxilia a população na escolha alimentar. Este artigo apresenta uma revisão sobre ácidos graxos trans, desde sua formação, efeitos para a saúde e as medidas atuais de controle da sua ingestão, enfatizando a rotulagem de alimentos. A busca de informações, relativa ao período de 1990 a 2012, foi realizada nos bancos de dados Scopus, PubMed, SciELO, Science Direct, Lilacs, bem como em sites oficiais nacionais e internacionais. Os unitermos utilizados em português e inglês foram: “ácidos graxos trans” e/ou “gordura hidrogenada”, conjugados à “rotulagem” e/ou “regulação” e/ou “legislação”. O controle dos ácidos graxos trans pode ser realizado pela diminuição de seu consumo por meio de medidas industriais, medidas individuais e coletivas, resultantes de um trabalho educativo, além de forças políticas. Em relação à rotulagem, mesmo existindo legislação brasileira que obrigue as indústrias a informarem a quantidade de ácidos graxos trans por porção em alimentos industrializados, observaram-se alguns questionamentos sobre como são disponibilizadas tais informações. Salienta-se que a efetiva diminuição dos ácidos graxos trans pode levar um tempo considerável, dada a adaptação cultural e tecnológica necessárias. Contudo, é uma medida importante, pois o resultado desse controle será a melhoria da saúde da população.

Plasma phospholipid fatty acid concentrations and risk of gastric adenocarcinomas in the European Prospective Investigation into Cancer and Nutrition (EPIC-EURGAST)

BACKGROUND

Epidemiologic data suggest that diet is a risk factor in the etiology of gastric cancer. However, the role of dietary fatty acids, a modifiable risk factor, remains relatively unexplored.

OBJECTIVE

The objective of this study was to determine the association of plasma phospholipid fatty acid concentrations, as biomarkers of exogenous and endogenously derived fatty acids, with the risk of gastric adenocarcinoma in a case-control study nested within the European Prospective Investigation into Cancer and Nutrition-Europe Gastric Cancer (EPIC-EURGAST).

DESIGN

Fatty acids were measured by gas chromatography in prediagnostic plasma phospholipids from 238 cases matched to 626 controls by age, sex, study center, and date of blood donation. Conditional logistic regression models adjusted for Helicobacter pylori infection status, BMI, smoking, physical activity, education, and energy intake were used to estimate relative cancer risks.

RESULTS

Positive risk associations for gastric cancer were observed in the highest compared with the lowest quartiles of plasma oleic acid (OR: 1.72; 95% CI: 1.01, 2.94), di-homo-γ-linolenic acid (OR: 1.92; 95% CI: 1.10, 3.35), α-linolenic acid (OR: 3.20; 95% CI: 1.70, 6.06), and the ratio of MUFAs to saturated fatty acids, as an indicator of stearoyl-CoA desaturase-1 enzyme activity (OR: 1.40; 95% CI: 0.81, 2.43). An inverse risk association was observed with the ratio of linoleic to α-linolenic acid (OR: 0.37; 95% CI: 0.20, 0.66).

CONCLUSION

These data suggest that a specific prediagnostic plasma phospholipid fatty acid profile, characterized mainly by high concentrations of oleic acid, α-linolenic acid, and di-homo-γ-linolenic acid, which presumably reflect both a complex dietary pattern and altered fatty acid metabolism, may be related to increased gastric cancer risk.

Fatty acid composition of Greek margarines and their change in fatty acid content over the past decades

Thirty-one brands of margarines from the Greek market were analyzed for their fatty acid composition including trans-fatty acids by gas chromatography. Trans fatty acids (TFAs) were found within the range of 0.16-0.97% of total fat content, with no sample found to have TFA in a concentration more than 1% of the total fat content. Increased levels of either saturated or cis-unsaturated was observed in each brand. Saturated, cis-monounsaturated and cis-polyunsaturated were found in the ranges of 11.26-51.75%, 22.98-60.37% and 12.09-56.30% of total fat content respectively, with mean values of 30.81 ± 10.40%, 34.41 ± 10.46% and 34.28 ± 14.02% of total fat. The chemical analysis of Greek margarines over the past decades has indicated that the TFA content of Greek margarines has declined over the past 20 years by approximately 95%.